This invention relates to a method of significantly reducing the levels of sulfites, sulfates, salts and fatty components in liquid protein hydrolysate. This invention further relates to the resulting purified protein product and fatty components.
Protein hydrolysate consists of a mixture which includes amino acids and short chain peptides resulting from the hydrolysis of various animal and vegetable proteins. These protein hydrolysates may also be obtained from bacterial or yeast cultures. See for example, Scharf et al., U.S. Pat. No. 4,627,983. Protein hydrolysates are also common by-products of other procedures such as the extraction of the blood anti-coagulate heparin from porcine hash gut or intestinal mucosa.
Purified protein products from protein hydrolysate have a multitude of potential uses such as cosmetic additives, nutritional ingredients for foods and beverages, foaming agents, additives to medicinal compounds to block bitterness, sources of amino acids, additives or replacements for infant formula, and use in artificial nutrition administered orally, internally, parenterally or intravenously.
Of particular interest in the present application is the use of protein purified from protein hydrolysates as a feed ingredient for livestock starter rations. For example, University feeding trials have shown that protein hydrolysates when evaporated to a slurry of 45% solids, prove to be an excellent source of protein for pig starter rations. This reduction of water content to 55% also has shown an added benefit of reduced or eliminated problems with spoilage. Preferably the protein hydrolysates are evaporated or reduced to a 5% or less water content for efficiency and economic purposes. Nutritional uses of the purified protein hydrolysate also include such specialty feeds as milk replacers for calf, piglet and other weaning mammals, protein extender for animal feed, an amino acid supplement, and flavor or protein enhancer for human food and pet food. However, without further purification, evaporation of water from the protein hydrolysate renders a final product with higher salt and sulfite concentrations making the end product unsatisfactory for many of these uses. Further purification becomes even more important when the protein hydrolysate is reduced to a dried product thus increasing the salt and sulfite concentrations even more.
For both economic and environmental reasons, productive use is now being made of an increasing percentage of the waste material generated as a result of the slaughter of animals, such as livestock. As mentioned above, a major use of livestock waste or other by-products is in the production of the blood anti-coagulant heparin. It has been estimated that over 90% of the heparin currently used as a blood anti-coagulant is obtained from porcine intestinal mucosa. (See U.S. Pat. No. 5,607,840.) An aqueous solution containing the mucosa from the livestock waste or by-products is chemically (either by acid or alkaline treatment) or enzymatically (by protease for example) hydrolyzed. The heparin is then extracted from the hydrolyzed mucosa by techniques known to those of skill in the art, such as selective sorption using an ionic exchange resin.
The solution containing the digested tissues includes high concentrations of salt to discourage or prevent constituents other than certain anionic or polyanionic materials such as the heparin, from sticking to the resin during the sorption of these materials. In addition, the mucosa and the digest solution also contain, as a rule, an additional salt component. This additional salt component is introduced into the solution in the form of an oxygen scavenger, bacteriostat or bacteriocide, typically sodium bisulfite, which is added to stabilize the raw material and to prevent bacterial growth.
It is known that, following column purification, the high residual concentration of salt in the digestion solution renders the unabsorbed portion of the digest largely useless for most practical purposes. The salt and sulfite levels make this protein sidestream less acceptable. While sulfites can serve as an effective source of sulfur in fertilizers, prolonged usage of this concentrated protein sidestream may become potentially toxic when repeatedly applied to soil. The sidestream may also be toxic to those animals or humans allergic to sulfites.
One method of reducing the salt level is to perform enzyme hydrolysis as an alternative to chemical treatment. For example, Van Gorp et al., U.S. Pat. No. 5,607,840 teach a method of preparing protein hydrolysates from livestock by-products such as pork intestines, with an enzyme selected from the proteolytic enzymes of the Subtilisin family. Van Gorp et al. teach the use of proteolytic enzyme at salt concentrations of less than 0.1 molar, however, the need for a bacterial growth inhibitor is still recognized. Further, even in the presence of such a bacterial growth inhibitor such as 0.5% (w/v) sodium metabisulfite, if the raw material is to be transported or stored, the raw material still needs to be maintained at an elevated temperature of between 55.degree. C. and 90.degree. C. to avoid rapid spoilage.
While other methods have been developed that will yield purified protein products from protein hydrolysates, these methods assume that the production of the protein hydrolysate is the ultimate goal, therefore the protein source is not stored or transported for a long period of time and the creation of the protein hydrolysate will immediately precede the purification process. See Kazumasa Ohtsuka et al., U.S. Pat. No. 4,130,555; Brule et al., U.S. Pat. No. 4,361,587; and Kinumaki et al., U.S. Pat. No. 4,294,856. The use of bacterial growth inhibitors such as bacteriostats or bacteriocides are not necessary when there is no storage, transport or other conditions leading to spoilage at issue.
One method of overcoming spoilage in transport after extraction of heparin is to evaporate the water in the protein hydrolysate to a water content of 55% or less. This has the additional advantage of reducing water content in the resulting protein hydrolysate thus reducing shipping costs and further lowering costs by lowering storage volumes needed for the same amount of protein. However, by reducing water content from approximately 82% (as is found in many commercially available protein hydrolysate available as by-products from the production of heparin) to 55% or less water content the sodium sulfite levels are also being concentrated. For example, a typical level of sulfite in an 18% solid by weight liquid protein hydrolysate is 2.5% to 3.5%. However, when this same 18% solid by weight protein hydrolysate is concentrated through evaporation of the water to a water content of 55% the sulfite concentration is increased to 6.25% to 8.75% in the concentrated product. This level of sulfite is found to be undesirable by many end product users and completely unacceptable by many more. For example, the protein hydrolysates as potential sources of nutrient become unpalatable with the presence of high sulfite levels when used in the pet food market. Further, the Association of American Feed Control Officials (AAFCO) (official publication at pages 196-197) restricts the use of sulfites in meats and vitamin BI sources.